Field
The present invention relates generally to electrical energy storage devices, and, more specifically, to the design of electrolyte for electrical energy storage devices, such as double-layer capacitors.
Description of the Related Art
Electrical energy storage cells are widely used to provide power to electronic, electromechanical, electrochemical, and other useful devices. Such cells include primary chemical cells, secondary (rechargeable) cells, fuel cells, and various species of capacitors, including ultracapacitors. Some characteristics of electrical energy storage cells include energy density, power density, charging rate, internal leakage current, equivalent series resistance (ESR), and ability to withstand multiple charge-discharge cycles. For a number of reasons, capacitors that can store relatively large amounts of charge, known as supercapacitors and ultracapacitors, have gained prominence among the various electrical energy storage cells.
Increases in operating voltage of ultracapacitors can provide enhanced energy storage and power capabilities. However, various components of the capacitor may exhibit instabilities when subject to operating conditions of increased voltage. For example, instabilities in one or more components of the capacitor may contribute to deterioration in capacitor performance, including but not limited to excessive capacitance fade and Equivalent Series Resistance (ESR) increases on cycling or in DC lifetime also referred to as calendar lifetime, self-discharge, pseudocapacity, and/or gas formation.